This invention relates to the field of catalysis. More specifically, the invention relates to a heterocatalyst system wherein the catalytic results stems from two catalyst types, a metal part and the metal combined with another catalytically active or inactive substance.
In the use of zeolites as molecular sieves and catalyst supports, a great effort has been made to improve the activity and selectivity of these catalysts by devising a heterocatalyst system with a zeolite acting as a catalyst and a metal deposited on or reacted in the formation of the zeolite, thus due to its molecular sieve function further enhancing the catalytic activity of the zeolite.
One example of such a heterocatalyst system is described in U.S. Pat. No. 4,444,898, wherein a metal complex is reacted with a hydroxyl group that is in a zeolite or molecular sieve pore, and used for carbonylation and hydrogenation catalysis. Among these systems are the rhodium reaction product with a hydroxyl group within a Type 13X or 13Y zeolite cage. U.S. Pat. No. 4,622,308 describes a catalyst for the production of hydrocarbons from the synthesis gas which comprises an iron-containing Fischer-Tropsch catalyst, a zeolite and at least one metal consisting from the group ruthenium, rhodium, platinum, palladium, iridium, cobalt and molybdenum. The zeolites used are preferably X zeolites, Y zeolite, and mordenite. The metal is present in amounts from 5 to 80 percent by weight, based on the combined weight of the iron oxide and zeolite. U.S. Pat. No. 4,623,632 describes a catalytic composite for the conversion of hydrocarbons comprising a non-acidic zeolite having deposited thereon catalytically effective amounts of a Group VIII metal component and a sufficient surface-deposited alkali metal to provide a surface-deposited alkali metal index of at least 10. Typical of the non-acidic zeolites are X zeolite, Y zeolite, L zeolite, and mordenite. U.S. Pat. No. 3,376,215 discloses a hydrocarbon conversion catalyst comprising a cocatalytic solid support containing a Group VIII metal, the support comprising (1) an adsorbant refractory inorganic oxide and (2) a mordenite zeolite. The mordenite zeolite has deposited thereon a metal selected from the class of alkali metals, alkaline earth metals and mixtures thereof.
European Patent Application 185,329 discloses dewaxing catalysts and a process employing silicoaluminumphosphate molecular sieves. The catalysts comprise at least (1) a silicoaluminumphosphate molecular sieve, and (2) optionally, and in the instance of hydrodewaxing, at least one hydrogenation component. The silicoaluminumphosphate molecular sieves are disclosed in U.S. Pat. No. 4,440,871. A general paper discussing heterocatalysts is the article by D. C. Bailey et al., entitled "Immobilized Transition-Metal Carbonyls and Related Catalysts," Chem. Rev. 81(2), 109-145 (1981).
Thus it can be seen in the prior art that it is known to combine metals with zeolites in order to produce heterocatalysts. U.S. Pat. No. 4,444,898, cited supra, discloses using such a heterocatalyst system for hydrogenation. However, it is also known in the art that zeolites X, L, Y and mordenite, as well as aluminumphosphate and silicoaluminumphosphate molecular sieves in general, have pore sizes less than or equal to about 9 Angstroms. Thus, their use for performing a catalytic shape-selective hydrogenation of a given selected molecule is limited by the pore size. In view of this, it would be desirable in the art to have a heterocatalyst system allowing for shape-selective hydrogenation of molecules having a diameter greater than about 9 angstroms.